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Old 10th March 2010, 10:38 PM   #1
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Default Using different transformer taps for each needed B+

I recently completed a mono block 2 stage PP design that required a 380V B+ for the finals and a 320V B+ for the phase splitter (2 stage design), and it works great.

The PS is a CLCRC with the CLC providing the 380V B+ and the remaining RC section providing the 320V B+.

My power transformer has 360-0-360 taps @ 140ma and 275-0-275 @ 40ma taps. The above topology uses the 360V taps only; I am not using the 275V taps for anything.

It just occured to me that I could have used the 275-0-275 V taps to separately rectifiy and smooth the 320V B+ for the phase splitter (it needs 9 ma) at the expense of one additional cap and a pair of diodes, leaving the 360-0-360 taps for the finals by themselves.

Is there any benefit to using separate PS transformer taps (if available) for each stage? It seems to me that decoupling between stages would be a little better...and perhaps allow me to squeeze a little more total VA out of the transformer.......anything else?
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Old 10th March 2010, 10:48 PM   #2
tomchr is offline tomchr  United States
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You'd limit the chance of inter-stage coupling via the power supply. That would reduce the probability of oscillations in many cases.

If one of your supplies is rectified with a tube and others are with diodes, I'd worry about the timing of the power supply sequencing.

I think the power (VA) limit of a transformer is mostly set by the core area so I doubt you'll get any significant amount of additional power out of the transformer by using the spare taps. A little bit maybe. But not a huge amount.

~Tom
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Old 10th March 2010, 10:54 PM   #3
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It's a no NFB triode PP design; both PS sections would be SS rectified.

thanks!

Something else to try, perhaps tonight....
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Old 10th March 2010, 10:59 PM   #4
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You would need to have some sort of filter for each winding. But certainly it makes it easier to decouple stages and probably most importantly, the phase splitter phase would be powered by a lower impedance than would be if driven by a CLCRC set-up. Not that it makes a huge impact in a driver.
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